1. Field of the Invention
The present invention relates to a radio communication apparatus for use in a base station or a mobile station in a mobile radio communication system of automobile phones, portable phones or cordless phones.
2. Description of the Related Art
FIG. 12 is a block diagram showing the circuit configuration of a conventional radio telephone apparatus. Specifically, in a transmitter system, a digitized voice signal or data signal is input to an encoder (COD) 11. In the encoder 11 the digital signal is encoded and compressed, and, where necessary, it is provided with an additional signal, thereby generating orthogonal signals (i.e. an I signal and a Q signal) for digital modulation. The orthogonal signals are subjected to digital filtering in route cosine roll-off filters 12a' and 12b' and unnecessary high-frequency components are removed. The resultant signals are converted to analog signals in digital-to-analog converters (DAC) 13a and 13b. The analog orthogonal signals are smoothed by low-pass filters (LPF) 14a' and 14b' and then input to multipliers 15a' and 15b'. In the multipliers 15a' and 15b', the analog orthogonal signals and orthogonal carrier signals are mixed to produce modulated carrier signals. The orthogonal carrier signal are produced such that a carrier signal generated by a frequency synthesizer (SYN) 51 is passed through a switch (SWG) 60 and then divided into two components and one of the two components is shifted by .pi./2 by a .pi./2 phase shifter 52. The modulated carrier signals output from the multipliers 15a' and 15b' are summed by an adder 16. The sum signal is delivered to a transmission power amplifier 19 through a band-pass filter (BPF) 17' and a variable attenuator 18', and it is amplified to a predetermined level. Then, the amplified modulated carrier signal is transmitted from an antenna 22 through a band-pass filter (BPF) 20 and a high-frequency switch (SW) 21.
On the other hand, in a receiver system, a modulated carrier signal received by the antena 22 passes through the switch 21 and is amplified by a low-noise amplifier (LNA) 31. The amplified signal passes enters a multiplier 34 via a band-pass filter (BPF) 32 and a variable attenuator 33. In the multiplier, the input modulated carrier signal is mixed with a local oscillation signal, which was generated from a frequency synthesizer 51 and delivered from a switch 60, and is frequency-converted to an intermediate frequency signal. Thereafter, the intermediate frequency signal is amplified by an intermediate frequency amplifier 35 and input to a frequency detector 36. After the amplified intermediate frequency signal is detected by the frequency detector 36, it is smoothed by an integrating discharger 37. As a result, a received base-band signal is demodulated. The base-band signal is digitized by an analog-to-digital converter (ADC) 38, and an unnecessary frequency component thereof is removed by digital filtering in a route cosine roll-off filter (RCROF) 39. The resultant signal is input to a decoder (DEC) 40. In the decoder 40, the received digital base-band signal is decoded to produce a digital voice signal or a digital data signal.
In the field of portable radio telephones and cordless radio telephones, it is an important object to reduce the size and weight and enhance the portability. It is another object to reduce the power consumption and increase the life of batteries.
However, the conventional radio telephone generally comprises an independent transmitter system and an independent receiver system. Thus, the circuit configuration of the entire apparatus is large and complex. In the prior art, individual circuits have been integrated in LSIs to reduce the size of the apparatus, but the number of chips is large and there is a limit in miniaturization of the entire circuits. In addition, there are circuits, such as filters, which are difficult to integrate, and this also limits the reduction in size and weight. Furthermore, the number of circuits is high and power consumption is also high accordingly. Thus, it is difficult to reduce the power consumption of the entire apparatus.